As a component of any ecosystem, a plant's biochemical activity and life processes are frequently intertwined with the activity of a variety of microorganisms that live in close proximity to the plant, i.e. microbes that live in proximity to the plant's roots or root system. Microbes in the soil in this area are influenced by the root and, conversely, the root is influenced by the microbes. This area of plant/microorganism interaction within the soil is known as the rhizosphere.
In addition to acquiring material from their soil environment, plants frequently exude various compounds into the same environment. Chemical communication and interaction frequently occurs between plants and microbes. Indeed, plants exude substances which can attract various microbes or repel microbes. The chemical interaction between the roots and microbes can both directly and indirectly affect systemic plant physiology.
Plants require a variety of raw materials and essential nutrients which, excluding a select few elements, must be obtained from the soil in which the plant is located. Typically, the nutrient uptake is carried out by or through a plant's roots or root system. Two nutrients that are uniformly required by plants in fairly large quantities are Nitrogen and Phosphorus. Although not always required, the symbiotic assistance of fungi often enhances many plants' uptake of these and other essential nutrients.
For example, Nitrogen and Phosphorus uptake is frequently facilitated through an association between the plant and one of various species of fungi inhabiting the rhizosphere. In a mycorrhizal association, a microbe fungus colonizes the roots of a host plant thereby engaging in a symbiotic relationship which benefits both organisms. This is done either intracellularly, as with arbuscular mycorrhizal fungi which actually penetrate plant cell walls, or extracellularly, as with ectomycorrhizal fungi which wrap around the epidermal cells of roots.
Recently much attention in plant ecophysiology research has been focused on studying the biology of the rhizosphere and the mycorrhizal association. The difficulty, however, is that the current methodological approaches, by their very nature, are inherently destructive or cannot otherwise be carried out under natural field conditions. For instance, the vast majority of methods require the removal of the root system from the soil. Further, these approaches are generally difficult to apply to large numbers of plants comprising a larger ecosystem.
A method is therefore needed to quantify and image the biological interactions of plants and fungi, and more specifically, mycorrhizal associations, without disturbing the plant or soil so that longitudinal studies can be repeatedly performed on the same plant and soil/microbe biological system. To date, no one has used radioisotope based techniques for examining the rhizosphere and, more specifically, mycorrhizal associations in the rhizosphere.